Tema 0: Transmisión de Datos Multimedia - UPV · Transmisión de Datos Multimedia -Master IC...

Transmisión de Datos Multimedia – http://www.grc.upv.es/docencia/tdm – Master IC 2007/2008

Tema 0:Transmisión de Datos MultimediaTema 0:Transmisión de Datos Multimedia

�Clases de aplicaciones multimedia

�Redes basadas en IP y QoS

Computer Networking: A Top Down Approach Featuring the Internet,

3rd edition. Jim Kurose, Keith Ross

Addison-Wesley, July 2004.

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isión de Datos Multimedia -Master IC 2007/2008

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What is multimedia?

� Definition of multimedia

� Hard to find a clear-cut definition

� In general, multimedia is an integration of text, graphics, still and moving images, animation, sounds, and any other medium where every type of information can be represented, stored, transmitted and processed digitally

� Characteristics of multimedia

� Digital – key concept

� Integration of multiple media type, usually including video or/and audio

� May be interactive or non-interactive

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Various Media Types

� Text, Graphics, image, video, animation, sound, etc.

� Classifications of various media types

� Captured vs. synthesized media

� Captured media (natural) : information captured from the real world– Example: still image, video, audio

� Synthesized media (artificial) : information synthesize by the computer– Example: text, graphics, animation

� Discrete vs. continuous media

� Discrete media: space-based, media involve the space dimension only– Text, Image, Graphics

� Continuous media: time-based, media involves both the space and the time dimension– Video, Sound, Animation

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Classification of Media Type

SoundSound VideoVideo

ImageImage

AnimationAnimation

TextText GraphicsGraphics

Captured

From real world

Synthesized

By computer

Discrete Discrete

Continuous Continuous

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Text

� Plain text

� Unformatted

� Characters coded in binary form

� ASCII code

� All characters have the same style and font

� Rich text

� Formatted

� Contains format information besides codes for characters

� No predominant standards

� Characters of various size, shape and style, e.g. bold, colorful

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Plain Text vs. Rich Text

An example of Plain text Example of Rich text

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Graphics

� Revisable document that retains structural information

� Consists of objects such as lines, curves, circles, etc

� Usually generated by graphic editor of computer programs

-4

-2

0

2

4

-4

-2

0

2

4

-10

-5

0

5

10

Example of graphics (FIG file)

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Images

� 2D matrix consisting of pixels

� Pixel—smallest element of resolution of the image

� One pixel is represented by a number of bits

� Pixel depth– the number of bits available to code the pixel

� Have no structural information

� Two categories: scanned vs. synthesized still image

Computer

software

Computer

software

Capture and

A/D conversion

Capture and

A/D conversion

Digital still imageDigital still image

Synthesized

image

Scanned

image

Camera

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Images (cont.)

� Examples of images

� Binary image – pixel depth 1

� Gray-scale – pixel depth 8

� Color image – pixel depth 24

Binary image

Gray-scale imagecolor image

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Video vs. Animation

� Both images and graphics can be displayed as a succession of view which create an impression of movement

� Video – moving images or moving pictures

� Captured or Synthesized

� Consists of a series of bitmap images

� Each image is called a frame

� Frame rate: the speed to playback the video (frame per second)

� Animation – moving graphics

� Generated by computer program (animation authoring tools)

� Consists of a set of objects

� The movements of the objects are calculated and the view is updated at playback

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Sound

� 1-D time-based signal

� Speech vs. non-speech sound

� Speech – supports spoken language and has a semantic content

� Non-speech – does not convey semantics in general

� Natural vs. structured sound

� Natural sound – Recorded/generated sound wave represented as digital signal

� Example: Audio in CD, WAV files

� Structured sound – Synthesize sound in a symbolic way

� Example: MIDI file

0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0 1 0 0 0- 0 . 2

- 0 . 1 5

- 0 . 1

- 0 . 0 5

0

0 . 0 5

0 . 1

0 . 1 5

0 . 2

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Networked Multimedia

� Local vs. networked multimedia

� Local: storage and presentation of multimedia information in standalone computers

� Sample applications: DVD

� Networked: involve transmission and distribution of multimedia information on the network

� Sample applications: videoconferencing, web video broadcasting, multimedia Email, etc.

InternetInternetVideo server

Image serverA scenario of multimedia networking

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Consideration of Networked Multimedia

� Requirements of multimedia applications on the network

� Typically delay sensitive

� end-to-end delay

� delay jitter:– Jitter is the variability of packet delays within the same packet stream

� Quality requirement

� Satisfactory quality of media presentation

� Synchronization requirement

� Continuous requirement (no jerky video/audio)

� Can tolerant some degree of information loss

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Technologies of Multimedia Networking

� Challenges of multimedia networking

1. Conflict between media size and bandwidth limit of the network

2. Conflict between the user requirement of multimedia application and the best-effort network

3. How to meet different requirements of different users?

� Media compression – reduce the data volume

Address the 1st challenge

� Image compression

� Video compression

� Audio compression

� Multimedia transmission technology

Address the 2nd and 3rd challenges

� Protocols for real-time transmission

� Rate / congestion control

� Error control

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Multimedia Networking Systems

� Live media transmission system

� Capture, compress, and transmit the media on the fly (example?)

� Send stored media across the network

� Media is pre-compressed and stored at the server. This system delivers the stored media to one or multiple receivers. (example?)

� Differences between the two systems

� For live media delivery:

� Real-time media capture, need hardware support

� Real-time compression– speed is important

� Compression procedure can be adjusted based on network conditions

� For stored media delivery

� Offline compression – better compression result is important

� Compression can not be adjusted during transmission

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Classes of multimedia applications

� Streaming stored audio and video

� Streaming live audio and video

� Real-time interactive audio and video

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Streaming Stored Multimedia: What is it?

1. videorecorded

2. videosent

3. video received,played out at client

Cum

ulat

ive d

ata

streaming: at this time, client playing out early part of video, while server still sending laterpart of video

networkdelay

time

t>0

100%

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Streaming vs. Download of Stored Multimedia Content

� Download: Receive entire content before playback begins

� High “start-up” delay as media file can be large

� ~ 4GB for a 2 hour MPEG II movie

� Streaming: Play the media file while it is being received

� Reasonable “start-up” delays

� Reception Rate >= playback rate. Why?

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Streaming Stored Multimedia: Interactivity

VCR-like functionality: client can pause, rewind, FF, push slider bar

• 10 sec initial delay OK• 1-2 sec until command effect OK• RTSP often used (more later)

timing constraint for still-to-be transmitted data: in time for playout

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constant bit rate video

transmission

Cum

ulat

ive d

ata

time

variablenetworkdelay

client videoreception

constant bit rate video

playout at client

client playoutdelay

buf

fere

dvi

deo

Streaming Multimedia: Client Buffering

� Client-side buffering, playout delay compensate for network-added delay, delay jitter

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Streaming Multimedia: Client Buffering

� Client-side buffering, playout delay compensate for network-added delay, delay jitter

bufferedvideo

variable fillrate, x(t)

constantdrain

rate, d

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Interactive, Real-Time Multimedia

applications: IP telephony, video conference, distributed interactive worlds

� end-end delay requirements:

� audio: < 150 msec good, < 400 msec OK

� includes application-level (packetization) and network delays

� higher delays noticeable, impair interactivity

� session initialization

� how does callee advertise its IP address, port number, encoding algorithms?

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Internet multimedia: simplest approach

audio, video not streamed:

� no, “pipelining,” long delays until playout!

� audio or video stored in file

� files transferred as HTTP object

� received in entirety at client

� then passed to player

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Progressive Download

� browser GETs metafile

� browser launches player, passing metafile

� player contacts server

� server downloads audio/video to player

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Streaming from a streaming server

� This architecture allows for non-HTTP protocol between server and media player

� Can also use UDP instead of TCP.

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Multimedia Over Today’s Internet

� TCP/UDP/IP: “best-effort service”

� no guarantees on delay, loss

� But multimedia apps requires QoS and level of performance to be effective!

� Today’s Internet multimedia applications use application-level techniques to mitigate (as best possible) effects of delay, loss

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Streaming Multimedia: UDP or TCP?

UDP

� server sends at rate appropriate for client (oblivious to network congestion!)

� often send rate = encoding rate = constant rate

� then, fill rate = constant rate - packet loss

� short playout delay (2-5 seconds) to compensate for network delay jitter

� error recover: time permitting

TCP

� send at maximum possible rate under TCP

� fill rate fluctuates due to TCP congestion control

� larger playout delay: smooth TCP delivery rate

� HTTP/TCP passes more easily through firewalls

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Multimedia, Quality of Service: What is it?

Multimedia applications: network audio and video(“continuous media”)

network provides application with level of performance needed for application to function.

QoS

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Improving QOS in IP Networks

� Thus far: “making the best of best effort”

� Future: next generation Internet with QoS guarantees

� RSVP: signaling for resource reservations

� Differentiated Services: differential guarantees

� Integrated Services: firm guarantees

� simple model for sharing and congestion studies:

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Principles for QOS Guarantees

� Example: 1Mbps IPphone, FTP share 1.5 Mbps link.

� bursts of FTP can congest router, cause audio loss

� want to give priority to audio over FTP

packet marking needed for router to distinguish

between different classes; and new router policy

to treat packets accordingly

Principle 1

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Principles for QOS Guarantees (more)

� what if applications misbehave (audio sends higher than declaredrate)

� policing: force source adherence to bandwidth allocations

� marking and policing at network edge:

� similar to ATM UNI (User Network Interface)

provide protection (isolation) for one class from

others

Principle 2

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� Allocating fixed (non-sharable) bandwidth to flow: inefficient use of bandwidth if flows doesn’t use its allocation

While providing isolation, it is desirable to use resources as efficiently as possible

Principle 3

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� Basic fact of life: can not support traffic demands beyond link capacity

Call Admission: flow declares its needs, network may block call (e.g., busy signal) if it cannot meet needs

Principle 4

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Summary of QoS Principles

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